In conventional additive or three-dimensional fabrication techniques, construction of a three-dimensional object is performed in a step-wise or layer-by-layer manner. In particular, layer formation is performed through solidification of photo curable resin under the action of visible or UV light irradiation. Two techniques are known: one in which new layers are formed at the top surface of the growing object; the other in which new layers are formed at the bottom surface of the growing object.
If new layers are formed at the top surface of the growing object, then after each irradiation step the object under construction is lowered into the resin “pool,” a new layer of resin is coated on top, and a new irradiation step takes place. An example of such a technique is given in U.S. Pat. No. 7,892,474. A disadvantage of such “top down” techniques is the need to submerge the growing object in a (potentially deep) pool of liquid resin and reconstitute a precise overlayer of liquid resin.
If new layers are formed at the bottom of the growing object, then after each irradiation step the object under construction must be separated from the bottom plate in the fabrication well. While such techniques eliminate the need for a deep well in which the object is submerged by instead lifting the object out of a relatively shallow well or pool, a problem with such “bottom up” fabrication techniques is that extreme care must be taken, and additional mechanical elements employed, when separating the solidified layer from the bottom plate due to physical and chemical interactions therebetween. For example, in U.S. Pat. No. 7,438,846, an elastic separation layer is used to facilitate separation of solidified material at the bottom construction plane. Other approaches, such as the B9Creator™ 3-dimensional printer marketed by B9Creations of Deadwood, S.D., USA, employ a sliding build plate. Such approaches introduce a mechanical step that complicates the apparatus, slows the method, and potentially distorts the end product. Accordingly, there is a need for alternate methods and apparatus for three-dimensional fabrication that can obviate the need for mechanical separation steps between the fabrication of successive layers.